Gaseous electron tube circuits



I l'A1-ILM. WITTENBERG GAsEous' ELECTRQN TUBE CIRCUITS May 2, 1950 fein/@yay ATTORNEY Patented May 2., 195() GASEOUS ELECTRON TUBE CIRCUITS Hubert H. Wittenberg, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application October 29, 1948, Serial No. 57,362

7 Claims. (Cl. 315-350) This invention relates to improvements in gaseous electron tube circuits, and finds application in periodic wave frequency dividing networks, variable frequency relaxation oscillators, and analogous systems.

It has previously been proposed to accomplish frequency division of a periodic electrical wave by utilizing the wave to charge a capacitor in a series of steps through a diode or other similar rectifying device. The arrangement may be such that, after a predetermined number of cycles of the applied wave have been impressed on the circuit, the voltage across the capacitor becomes suilicient to unblock or fire a normally nonconducting electron tube device, such as a gaseous electron tube, a start-stop multivibrator, or the like, through which device the capacitor may then discharge rapidly to provide an output voltage pulse at a submultiple of the frequency of the applied wave. A system of this kind requires at least two tubes for each stage of frequency subdivision, and where several such stages are required, the number of tubes involved is corre spondingly large. Moreover, where it is required to provide a variable factor of frequency subdivision, systems of the foregoing-type do not always have the requisite flexibility.

` A specialized application of frequency division is encountered in the synchronization or frequency control of relaxation oscillators. In a well known type of relaxation oscillator, a capacitor is connected in parallel with the plate circuit of a gaseous electron tube, andarranged to be charged at a predetermined rate through a control resistor to obtain a substantially lin'- early changing voltage across the resistor. When the voltage on the capacitor is sufficient to cause the gas tube to conduct current, the capacitor 4 discharges rapidly through the tube, resulting in a sufticient drop in voltage to deenergize the tube, thus initiating a new cycle of operation. Since the plate voltage at which the gas tube will begin to conduct current is, in part, dependent on the grid voltage of the tube, such oscillators can be synchronized to operate at a submultiple of the frequency of a master control oscillator by supplying a synchronizing signal from the master oscillator to the grid of the relaxation oscillator tube. With the natural or free-running frequency of the relaxation oscillator adjusted to be near the desired submultiple of the frequency of the master oscillator, the signals from the master oscillator can be adjusted in amplitude until the relaxation oscillator will lock in'at exactly the desired submultiple of the master oscillator frequency. However, the natural frequency of conventional relaxation oscillators cannot be changed by any large amount without altering the waveshape ofthe output voltage, and hence it is quite diiiicult to design a relaxation oscillator which can be synchronized at different frequencies without having undesirable changes in the waveshape of the output voltage.

It is, accordingly, a principal object of the present invention to provide improved, variable frequency, gaseous electron tube control systemsB Another object of the invention is to provide an improved frequency dividing system of the gaseous electron tube type.

A further object of the invention is to provide an improved, wide range, frequency dividing sys-V tem requiring a minimum number of circuit elements.

Another object of the invention is to provide an improved relaxation oscillator having a readil variable operation period. ,z

1A further object of the invention is to provide an improved gaseous electron tube relaxation oscillator which is readily susceptible to syn# chronization at a submultiple frequency of -a control signal.

According to the invention, the foregoing and other objects and advantages are attainedby utilizing a tetrode or other multi-grid type of gaseous electron tube, with the biasing voltages for the tube so adjusted that the tube will draw control grid current during periods of anode cur'- rent flow. Under these conditions, a capacitor connected between the cathode and the control grid of the tube can be charged and discharged through the control grid circuit of the tubeto regulate the voltage at the control grid, and, as 'a result, the operational periods of the tube may be varied at willin any one of several different Ways.

A more complete understanding of the inven tion may be had by reference to the following description of illustrative embodiments of the invention, when considered in connectionV with the accompanying drawing, in which:

Figure 1 is a circuit diagram showing a fre quency dividing system arranged in accordance with the invention, Figure 2 is a circuit diagram of a relaxation oscillator, arranged in accordance with the 'in vention, Figure 3 is a graph of one of the grid voltage# plate voltage characteristics of a typical gas tetrode tube, Y Figure 4 is a graph of one .of the vgrid volta'ga grid current characteristics of a typical gas tetrode tube,

Figure 5 is a graphical representation of the operation of the circuit shown in Figure 1,

Figure 6 is a graph showing the effect on output frequency of varying the shield grid voltage in the circuit of Figurel,

Figure 7 is'l a graph showing .the effecten output frequency of varying theI primary control grid voltage in the circuit of Figure l,

Figure 8 is a graph showing the effect on output" frequency of varying the controifgr'id-tocathode' capacity in the circuit of Figure 1, and

Figure 9 is a graph showingthe effect onont-4 put frequency of varying the g'd circuit resiste' ance in the circuit of Figure 1.

Referring to the drawings; the invention willv rst be described as applied to an alternating current frequency dividing network, and accordinsb'. there is Sherri, in Figure Le frequency f dividinesy'stm a1'1`far-1eedY in afordame With; the inv ,rftioa Such ai erstenmal?. ir'iglud. a nfiuiltf gridggaseous; electron discharge tube, such as a tet'od Ill, having` a cathode I2, a control grid Mipaf shield grid i3, and an anode I3.v n source 2p o f variable negative biasingvoltage isl provided for the shield grid i6, such as a battery 2l having a. potentiometer 22 connected in parallel therewith; while a source 24 of variable positive bi'asing voltage is provided for the control grid f4, such as a second battery 25 having a potentiometer x26 connected in parallel therewith. Avoltage control capacitor 28 is connected between the control grid i4 and the Ycathode-l2 of they tube lhfand a capacitor charging control element, sii'chas va resistor 33, is connected between the ontrol grid i4 and the bias Voltage source 24'. While the element 3G has been shown as a resistor; it will be obvious that other impedance elements, through which the capacitor -23 can vbe charged, might be used in its place; The shield grid I3 may be connected to the biassbur'ce 20 through an isolating resistor 3 l. For convenience of discussion, the Vbias voltage sources for ith'e tube L0 have beenshown asin'dividu'al sources 20 and 24, although it will be apparentvthat a y'single Source of volta'gecould as well be used.

TheY anode lcircuit of the tube VHl is Aseen to include voltage input terminalsl 32, 34, through .inducir an alternating voltager ofv any desired .frequehcy may be applied to the systemr and an output impedance,V such as a resistor 3E, across Vl'hieh. a divided frequency output may be. ob'- taiined at a pair of .outputl terminals .3.3, 4c..

ine operation o f the circuit of Figure-lean best be Mexplained by reference to Figures 3 throughS of the accompanying drawing, in which Figures 3 and 4 show two .of the characteristic 4curves for a typical gas tetrode tube 'of a type suitable for the circuit of Figure 1, while Figures 5 through, 9 show certain ofthe operational characteristics of the circuit itself, Y

As wasA previously mentioned, the -shield grid voltage `obtained from the potentiometer 22de made suiiciently negative with respect to the cathode so that a positive control ,grid voltage will be required to iire the tube L0'. The relation between control grid voltage and anode voltage for a.vr typical `'gas tetrode, operated with a negative shield grid voltage, is shown by the curveof Figure 3, wherein anode voltage is plotted as the y ordinateagainst control grid voltage `as the abscissa. is an example, it can be assumed that the maximum positive voltage which ,will be appliedtp the anode 4circuitof thetube l t hrough the terminals 32, 34, is some predetermined Epi in the graph of Figure 3, and the corresponding grid voltage, at which the tube I0 will re, will be some positive voltage When the circuit of Fig. 1 is to be operated as a frequency divider, the control grid bias voltage from the source 24 will be adjusted to a value En substantially equal to or slightly greater than the critical voltage En. Under these conditions,v when apositive half cycle o'f voltage occurs at the input terminals 32, 34, the tube I will nre, and current will flow in the anode circuit of the tube le. When anode current ilows, the control grid it will also collect a current, the magnitude 0f which will be dependent, in part, on the voltage supplied to the control grid. This is shown in the graph of Figure 4, wherein control grid current is plotted against' control grid voltage for one particular value of anode current, it being understood that the curvev of Figure 4 is only one of a family of similar curves which might be plotted, each of which would represent a grid voltage-'grid current characteristic for the tube lil for a given value ci anode current.

It will be appreciated that, in order to deter* mine the actual voltage at the' control grid I4 during-grid current now, a load line L must be drawn on the graph of Figure i to determine the eiect of the particular grid resistor 30 which is being used. The'load line will originate at the point of maximum, grid supply voltage En, and will have a slope determined bythe magnitude cf the grid resistorused. The intersection of the load line L with the characteristicA grid voltage'- grid current curve will give the actual grid voltage and grid current forI the tube l under operating conditions. From Figure 4, it will be seen that the actual voltage Eg at the control grid I4 of the tube IS during grid current iiow'will be considerably less than the critical grid voltage En which is necessary to lire the tube under the assumed conditions, and hence the voltage on the capacitor 28 must decrease to correspond with the new voltage obtaining at the control grid. The 'now of grid current in the tube I0 will be elective'to discharge the gridv capacitor 28 from thev voltage En, which existedat the grid of the tube prior to iring thereof, to a voltage equal to the actual control grid voltage Eg on the tubeduring anode and grid current flow.

As the input voltage at the terminals 32, 34 of the circuit of Figure Y1 vchangesfrom a positive to a negative value, the` tube lll Will cease to drawcurrent,andA the capacitor 2S will begin to chargefrom the bias source 24 through the resistor 39;.v However, this new of chargingcurrent through the resistor Si? will hold the voltage Eg at the control grid I4 belowthecritical voltage En for a time determined by the 'time constant of theresistor Sil and the capa-citer 2 8. Hence, on the next positive. half cycle c f anode voltage, the tube cannot conduct lcurrent because the control grid voltageEg will be Abelow the critical value Egl vindicated in Figure. '3.

This action 'is more clearly illustrated in the operational graph of Figure 5, in which thecurve Ep represents several cycles of; alternating voltage such as might be applied to the circuit of Figure 1 throughthe termina-1s 32, 34, the curves Egi represent the critical grid voltage required to Tire the tube IIJ during each positive cycle of anode voltage for a given negative shield grid voltage, and the line lili;A represents the actual voltage `at the -grid of the tube lll. In Figure 5, it may be assumed that, at sometime to during the 'first positive Vhalf cycle of alternating voltage shown, the capacitor 28 will become sufficiently charged to permit the tube l0 to lre, and, consequently; to draw anode and grid current in the manner previously described. As shown by the control grid Voltage line Eg in Figure 5, when the tube I0 fires at the time to, the control grid voltage will drop from the critical Value Egi to the value determined from the intersection of the load line L with the characteristic curve in Figure 4.

During the next two positive half cycles of input voltage Ep, `the grid voltage Eg remains below the critical level Egi due to charging of the capacitor 28. In the example illustrated by Figure 5, on the fourth positive half cycle of input voltage, the capacitor 28 becomes suiciently charged to permit the tube to fire again. It will be understood that, when the tube I0 fires, a pulse of voltage will be developed across the output resistor 36, and in the example shown, the frequency of this output pulse will be one-third of thevfrequency of the input voltage.

The frequency of the signal available at the terminals 33, 4U of Figure 1 can be controlled by varying the control grid resistor 30,- the control grid capacitor 28, the shield grid bias voltage from the potentiometer 22, or the control grid bias voltage from the potentiometer 26. Variations of either the capacitor 28 or the resistor 3U vary the time constant of the resistor-capacitor combination 36-28, and, consequently, the rate-of-rise of the exponential grid voltage curve Eg of Figure 5. In Figure 6 of the drawing, in which grid-to-cathode capacity is plotted as the ordinate against output frequency as the abscissa, there is shown the variation in the output frequency'which can be obtained by varying the capacitor 28 in a typical circuit arranged as shown in Figure l. Figure 7 shows the analogous effect on output frequency of variation of the resistor 30 in Figure l.

l 'Theeect on the output frequency which can be obtained by varying the shield grid and the control grid bias voltages in a typical case, is shown in Figures 8 and 9, respectively. Making the shield grid bias voltage more negative raises the critical control grid Voltage required to fire the tube l0 for a given value of anode voltage, Iand hence lowers the output frequency. This is illustrated in Figure 8, wherein the shield grid bias voltage is plotted as the ordinate against the output frequency as the abscissa. As seen in Figure 8, if the shield grid bias is made sulficiently negative, no output Will be obtained at the terminals 38, 40. As the shield grid bias voltage approaches Zero, the critical grid voltage En also approaches Zero, and if the shield grid bias voltage is made suiiiciently negative, output pulses will be Iavailable at terminals 38, 40 for every cycle of applied anode voltage.

In the graph of Figure 9, wherein control grid bias voltage is plotted as the ordinate against output frequency as the abscissa, the effect of variations in control grid bias voltage on the output frequency of the system is shown. As is indicated in Figure 9, for a given value of shield grid voltage, the frequency of the output will be decreased by making the control grid bias supply voltage less positive.

As was previously mentioned, the principles of the invention are applicable to synchronization and/or frequency control of a relaxation oscillator, and accordingly, in Figure 2 of the drawing, there is shown an illustrative arrangement of one such embodiment of the invention. The shield grid and the control grid circuits for the system of Figure 2 are similar to those which have already been described for the circuit of Figure 1, with the exception that a pair of input termi-- nals 33, 35 may be provided in the grid circuit; as shown, Vthrough which a synchronizing signal may be applied to the system if desired. The anode circuit ofthe tube I0 is provided with a capacitor 31 connected-between the anode and the cathode of the tube, and a D. C. supply volt-- age source, illustrated as a battery 39, is lprovided for charging the capacitor 31 through an output resistor 36.

The operation of the circuit of Figure` 2 will be similar in many respects to that of the-circuit of Figure l. In this case, however, the periodically varying anode voltage for the tube |-0 will be obtained from the periodic charge and discharge of the capacitor 31. As is the usual case with so-called relaxation oscillators, the capa'c'i tor 31 will be charged from the battery 39 through the resistor 36 at a rate depending on thevolta'ge of the battery 39 and the time constant of the resistor-capacitor combination which comprises the resistor 36 yand the capacitor 31.

In the circuit of Figure 2, when the voltage across the capacitor 31 has reached a predetermined valu-e, (corresponding to the maximum positive voltage Epi applied to the anode in the circuit of Figure 1), the tube I0 will re provided the proper critical voltage exists at the control grid I4 of the tube. However, as was explained,I the control grid voltage is dependent on thecon dition of the capacitor 28 at any one instant, and accordingly, if the time constant of the anode circuit is less than that of the grid circuit, "the frequency of oscillation will be controlled by the grid circuit. When the voltage on the` capacitor 28 reaches the critical level necessary to r the tube i0 for a given voltage across the capacitor 31, tlie capacitor 31 will discharge through the anode circuit of the tube I0, while the capacitor 28 will discharge through the grid circuit as'was previously described. The discharge of the caf pacitor 31 will cause the anode voltage of the tube lll to drop sufficiently to extinguish the anode current, whereupon the charging of the capacitors 28 and 31 will again take place in the obvious manner. If desired, the relaxation osci1- lator shown in Figure 2 may be permitted to operate at some natural frequency selected by adjusting the shield grid bias voltage, the control grid bias voltage, the resistor 30, the capacitor 28, or it may be synchronized to operate at a submultiple of the frequency of a signal applied through the terminals 33, 35 to the grid circuit of the tube. In the latter case, the frequency of the periodic voltage wave at the output terminals may be set to any of the elements 22, 26, 28 or 30 of the circuit. Since the natural frequency of the relaxation oscillator circuit shown in Figure 2 can be varied in any one of four different ways, without altering any of the plate circuit parameters, it is apparent that synchronization of the oscillator at a submultiple of any one of a wide range of input frequencies can readily be affected Without adversely affecting the wave shape of the output signal from the oscillator.

Since many changes could be made in the circuits shown and described, all within the scope and spirit of the invention, the foregoing is to be construed as illustrative and not in a limiting sense.

What is claimed is:

1. A gaseous electron tube circuit comprising a gaseous electron tube having an anode, a cath- 1f Hai-wishieidgnid, andlacontroligridramd includA ingr :c control gridcrenitfon said tuhermeans for mintaiining said shield: grid at ajpnedetermineds matiz-potentiak relative to said. cathode. Said eontroltgri'dz circuit.: comprising' (1)? asource of -loltazge positivewitlr respect toisaidrcathode, (1 2):

npacitor connected;.lcetvenA said control grid said: cathode, vvand. (It).l a continuouslyconv ducting capacitor. charging controlfelement connocted. between said; source andsaid control grid,

vand means for applying a periodically. varying;4

ywattage: to said-tube between said anode andsaid thade,

tftrcircuit as defined in claimv l wherein. said element.. comprises a resistor..

3a A gaseous electron tube control network adapted-.for usewith a multi-grid gaseouselectron tubs?,k said; netwerk: comprising an anode circuit, a

Yratiatum circuit, and a plurality of grid. circuits, fonsuppl-ying aperiodically varyingyoltage Atmsaid network: through said anode. and cathode, circuits.- means for maintainingone, of. saidA4 grid circuits atapredetermined negative potential relatiuestQ-said-cathode circuit,.means including auoltc source for applying a biasing voltage positive.

withutespectv` to said cathode to. another one o A. A. gaseous electron .tube circuit comprising @gaseous electron tube having an anode,` a cath.-

rifletta.shield` grid, and a control grid and' including, a control grid circuit for saidtuoe, means for maintaining. said shield grid at a predetermined .negative potential relative to said cathode, said control" grid circuit comprisingk ('1')- a source of `voltage .positive with respect to said control' grid and .said cathode, (-2) a. capacitor connected between said controlrgrid and said cathode, and. (3)'- a. 'continuously' conducting capacitor charging; control elementy:connettedaA betweeml said sourcey and. said:.controlY grid;M an. output circuit for saidx tulle comprising an mnedanceccnnected 'to' said: .anode and', means for supplying ra;pczrlcdicel1M warring-voltage to said, tugbe through. saiitimrv pedance..

5. Acircuit as rdeined claixnewhereinfsad element comprises;-a-v resistor.

A, gaseous electron tube: circuit. comprisim;

a gaseousj eleonora; tube having ananede, acath odeasshieldi vgridsanda. control grid and would -a control grid; circuit, for, said Ytu'oefand.an, amide circuit.. for said tube,i nieansior maintaim. ius; said shield grid ata predetermined negative. potential relative; to,l said-cathode, said control' grid circuit comprising. (i). .a..sourco of. uoltage. positive-- with respect tol said: cathode, t2) an pacitor: connected `leetvsieen said. corrtrolagridaud. said cathode, and` (-3.)y a. capacitor charging.- com trol element. connected. between saidsollrce and said control grid, said anode circuit. comprising (1)- a capacitor` connectedI between. said anode andsaid. cathode, (.29A a source of voltage,L and (3) an. impedance, said last.. named source .and said impedance.- bcing, serially connected.. between said. anode and s aidvcathode.

A` circuit asy claimed nclairnA 6= wherein said element, comprises a. resisten*v and wherein said impedance comprises a.. resistor.

H. `wrr'rmrBEPJG.,

REEERENQES vclulsn The following referencesY are oflrecord2 in the 

